The role of secondary hyperparathyroidism in the regulation of electrolyte transport is being studied in the rat with chronic renal failure. Renal failure is produced by 7/8th nephrectomy. Hyperparathyroidism is enhanced by feeding a low calcium - high phosphorous diet for 3-4 weeks. Regulation of urinary excretion of Na ion, H2O, HCO-3 and phosphate has been found to be increased by PTH in uremic rats. Parathyroidectomy reduces excretion of these electrolytes and water. We plan to study the transport of these same electrolytes in rats with chronic glomerulonephritis, a model in which the surviving nephrons may not undergo hypertrophy and which simulates chronic renal disease in man more closely. We also plan to study the possible role of PTH in causing secretion by the renal tubules. This will be done in uremic rats by perfusing isolated segments of the proximal tubule with Ringer's solution. 32P will be infused intravenously and entry of 32P into the lumen will be measured in the collected perfusate. The same measurements will be made after parathyroidectomy. The purpose of these projects is to determine the role of PTH in regulating electrolyte excretion in chronic renal disease.